feat: text to image vLLM Omni (#5912)

Signed-off-by: ayushag <ayushag@nvidia.com>

components/src/dynamo/vllm/args.py

@@ -265,7 +265,7 @@ def parse_args() -> Config:
         "--stage-configs-path",
         type=str,
         default=None,
-        help="Path to vLLM-Omni stage configuration YAML file. Required for --omni.",
+        help="Path to vLLM-Omni stage configuration YAML file for --omni mode (optional).",
     )
     parser.add_argument(
         "--store-kv",
@@ -388,9 +388,9 @@ def parse_args() -> Config:
             )
 
     # Validate omni worker requirements
-    if args.omni and not args.stage_configs_path:
+    if args.stage_configs_path and not args.omni:
         raise ValueError(
-            "--stage-configs-path is required when using --omni. "
+            "--stage-configs-path is only allowed when using --omni. "
             "Specify a YAML file containing stage configurations for the multi-stage pipeline."
         )
 
@@ -452,7 +452,8 @@ def parse_args() -> Config:
     config.request_plane = args.request_plane
     config.event_plane = args.event_plane
     config.enable_local_indexer = not args.durable_kv_events
-    config.use_vllm_tokenizer = args.use_vllm_tokenizer
+    # For omni mode, use vLLM (AsyncOmni) tokenizer on backend
+    config.use_vllm_tokenizer = args.use_vllm_tokenizer or args.omni
     config.sleep_mode_level = args.sleep_mode_level
     # use_kv_events is set later in overwrite_args() based on kv_events_config
 

components/src/dynamo/vllm/main.py

@@ -1215,18 +1215,12 @@ async def init_omni(
     component = runtime.namespace(config.namespace).component(config.component)
     generate_endpoint = component.endpoint(config.endpoint)
 
-    # Load default sampling params from model config (same as other workers)
-    default_sampling_params = (
-        config.engine_args.create_model_config().get_diff_sampling_param()
-    )
-    logger.info(f"Loaded default sampling params: {default_sampling_params}")
-
     # Initialize OmniHandler with Omni orchestrator
     handler = OmniHandler(
         runtime=runtime,
         component=component,
         config=config,
-        default_sampling_params=default_sampling_params,
+        default_sampling_params={},
         shutdown_event=shutdown_event,
     )
 
@@ -1241,11 +1235,9 @@ async def init_omni(
         return
 
     # TODO: extend for multi-stage pipelines
-    # Register as Chat endpoint for text-to-text generation
-    # Use Tokens input since we're doing token-based processing
     await register_llm(
-        ModelInput.Tokens,
-        ModelType.Chat,
+        ModelInput.Text,
+        ModelType.Images,
         generate_endpoint,
         config.model,
         config.served_model_name,
@@ -1254,7 +1246,6 @@ async def init_omni(
 
     logger.info("Starting to serve Omni worker endpoint...")
 
-    # Create health check payload (extracts BOS token from AsyncOmni)
     health_check_payload = (
         await VllmOmniHealthCheckPayload.create(handler.engine_client)
     ).to_dict()

components/src/dynamo/vllm/omni/omni_handler.py

 # SPDX-FileCopyrightText: Copyright (c) 2025-2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
 # SPDX-License-Identifier: Apache-2.0
-
-"""Omni handler for text-to-text generation using vLLM-Omni orchestrator."""
-
 import asyncio
 import logging
+import time
 from typing import Any, AsyncGenerator, Dict
 
 from vllm import SamplingParams
-from vllm.inputs import TokensPrompt
 from vllm_omni.entrypoints import AsyncOmni
+from vllm_omni.inputs.data import OmniTextPrompt, OmniTokensPrompt
 
 from dynamo.vllm.handlers import BaseWorkerHandler, build_sampling_params
 
@@ -32,10 +30,6 @@ class OmniHandler(BaseWorkerHandler):
             f"Initializing OmniHandler for multi-stage pipelines with model: {config.model}"
         )
 
-        # Initialize AsyncOmni with stage configuration
-        # Note: stage_configs_path is validated as required in args.py
-        logger.info(f"Using stage config from: {config.stage_configs_path}")
-
         omni_kwargs = {
             "model": config.model,
             "trust_remote_code": config.engine_args.trust_remote_code,
@@ -54,95 +48,242 @@ class OmniHandler(BaseWorkerHandler):
         self.config = config
         self.model_max_len = config.engine_args.max_model_len
         self.shutdown_event = shutdown_event
+        self.use_vllm_tokenizer = config.use_vllm_tokenizer
         logger.info("OmniHandler initialized successfully for text-to-text generation")
 
     async def generate(
         self, request: Dict[str, Any], context
     ) -> AsyncGenerator[Dict, None]:
-        """Generate text using AsyncOmni orchestrator. Currently supports text-to-text only."""
+        """Generate outputs using AsyncOmni orchestrator with OpenAI-compatible format.
+
+        Supports text-to-text and text-to-image generation based on stage configuration.
+        Returns OpenAI-compatible streaming chunks with detokenized text.
+        """
         request_id = context.id()
         logger.debug(f"Omni Request ID: {request_id}")
 
-        # Extract token_ids from internal protocol format
+        if self.use_vllm_tokenizer:
+            async for chunk in self._generate_openai_mode(request, context, request_id):
+                yield chunk
+        else:
+            async for chunk in self._generate_token_mode(request, context, request_id):
+                yield chunk
+
+    # Not used right now
+    async def _generate_token_mode(self, request, context, request_id):
+        """
+        This mode returns token-ids as output
+        Text input -> Token-ids output
+        """
         token_ids = request.get("token_ids")
-        if not token_ids:
-            logger.error(f"Request {request_id}: No token_ids found in request")
+        prompt = OmniTokensPrompt(token_ids=token_ids)
+        num_output_tokens_so_far = 0
+        try:
+            async for stage_output in self.engine_client.generate(
+                prompt=prompt,
+                request_id=request_id,
+            ):
+                vllm_output = stage_output.request_output
+
+                if not vllm_output.outputs:
+                    logger.warning(f"Request {request_id} returned no outputs")
+                    yield {
+                        "finish_reason": "error: No outputs from vLLM engine",
+                        "token_ids": [],
+                    }
+                    break
+
+                output = vllm_output.outputs[0]
+                next_total_toks = len(output.token_ids)
+
+                out = {"token_ids": output.token_ids[num_output_tokens_so_far:]}
+
+                if output.finish_reason:
+                    out["finish_reason"] = self._normalize_finish_reason(
+                        output.finish_reason
+                    )
+                    out["completion_usage"] = self._build_completion_usage(vllm_output)
+                    logger.debug(
+                        f"Completed generation for request {request_id}: "
+                        f"{next_total_toks} output tokens, finish_reason={output.finish_reason}"
+                    )
+
+                if output.stop_reason:
+                    out["stop_reason"] = output.stop_reason
+
+                yield out
+                num_output_tokens_so_far = next_total_toks
+
+        except GeneratorExit:
+            # Shutdown was triggered during generation
+            logger.info(f"Request {request_id} aborted due to shutdown")
+            raise
+        except Exception as e:
+            logger.error(f"Error during generation for request {request_id}: {e}")
             yield {
-                "finish_reason": "error: No token_ids in request",
+                "finish_reason": f"error: {str(e)}",
                 "token_ids": [],
             }
-            return
 
-        logger.info(
-            f"Request {request_id}: Generating text for {len(token_ids)} input tokens"
-        )
+    async def _generate_openai_mode(self, request, context, request_id):
+        """
+        This mode returns OpenAI-compatible streaming chunks
+        Text input -> Text output / Image output
+        """
+
+        # (ayushag) TODO: Support all type of OmniPrompt. Right now it works for only text prompts
+        # (ayushag) TODO: Document all I/O formats from vllm omni
+        # OmniText prompt support additional negative prompts as well. need to support that as well.
+        # Support multimodal content as well. That will involve  applying tokenizer to the prompt and loading images. Follow general multimodal support pattern.
+        prompt = self._extract_text_prompt(request)
+        prompt = OmniTextPrompt(prompt=prompt)
 
         # Build sampling parameters from request
-        sampling_params = self._build_sampling_params(request)
-        sampling_params_list = [sampling_params]
+        # (ayushag) TODO: Need to add proper multi-stage sampling param support
+        # sampling_params = self._build_sampling_params(request)
+        # sampling_params_list = [sampling_params]
 
-        tokens_prompt: TokensPrompt = {
-            "prompt_token_ids": token_ids,
-        }
+        previous_text = ""
 
         async with self._abort_monitor(context, request_id):
             try:
-                num_output_tokens_so_far = 0
-
                 async for stage_output in self.engine_client.generate(
-                    prompt=tokens_prompt,  # Pass TokensPrompt format
+                    prompt=prompt,
                     request_id=request_id,
-                    sampling_params_list=sampling_params_list,
+                    # sampling_params_list=sampling_params_list,
                 ):
-                    # stage_output is OmniRequestOutput
-                    # For text generation: stage_output.request_output is a single vLLM RequestOutput
                     if (
                         stage_output.final_output_type == "text"
                         and stage_output.request_output
                     ):
-                        vllm_output = stage_output.request_output
-
-                        if not vllm_output.outputs:
-                            logger.warning(f"Request {request_id} returned no outputs")
-                            yield {
-                                "finish_reason": "error: No outputs from vLLM engine",
-                                "token_ids": [],
-                            }
-                            break
-
-                        output = vllm_output.outputs[0]
-                        next_total_toks = len(output.token_ids)
-
-                        out = {"token_ids": output.token_ids[num_output_tokens_so_far:]}
-
-                        if output.finish_reason:
-                            out["finish_reason"] = self._normalize_finish_reason(
-                                output.finish_reason
-                            )
-                            out["completion_usage"] = self._build_completion_usage(
-                                vllm_output
-                            )
-                            logger.debug(
-                                f"Completed generation for request {request_id}: "
-                                f"{next_total_toks} output tokens, finish_reason={output.finish_reason}"
-                            )
-
-                        if output.stop_reason:
-                            out["stop_reason"] = output.stop_reason
-
-                        yield out
-                        num_output_tokens_so_far = next_total_toks
+                        # Text generation (LLM stage)
+                        chunk = self._format_text_chunk(
+                            stage_output.request_output,
+                            request_id,
+                            previous_text,
+                        )
+                        if chunk:
+                            # Update previous_text for delta calculation
+                            output = stage_output.request_output.outputs[0]
+                            previous_text = output.text
+                            yield chunk
+
+                    elif (
+                        stage_output.final_output_type == "image"
+                        and stage_output.images
+                    ):
+                        # Image generation (diffusion stage)
+                        chunk = self._format_image_chunk(
+                            stage_output.images,
+                            request_id,
+                        )
+                        if chunk:
+                            yield chunk
 
             except GeneratorExit:
-                # Shutdown was triggered during generation
                 logger.info(f"Request {request_id} aborted due to shutdown")
                 raise
             except Exception as e:
                 logger.error(f"Error during generation for request {request_id}: {e}")
-                yield {
-                    "finish_reason": f"error: {str(e)}",
-                    "token_ids": [],
+                yield self._error_chunk(request_id, str(e))
+
+    def _format_text_chunk(
+        self,
+        request_output,
+        request_id: str,
+        previous_text: str,
+    ) -> Dict[str, Any] | None:
+        """Format text output as OpenAI chat completion chunk."""
+        if not request_output.outputs:
+            return self._error_chunk(request_id, "No outputs from engine")
+
+        output = request_output.outputs[0]
+
+        # Calculate delta text (new text since last chunk)
+        delta_text = output.text[len(previous_text) :]
+
+        chunk = {
+            "id": request_id,
+            "created": int(time.time()),
+            "object": "chat.completion.chunk",
+            "model": self.config.served_model_name or self.config.model,
+            "choices": [
+                {
+                    "index": 0,
+                    "delta": {
+                        "role": "assistant",
+                        "content": delta_text,
+                    },
+                    "finish_reason": self._normalize_finish_reason(output.finish_reason)
+                    if output.finish_reason
+                    else None,
                 }
+            ],
+        }
+
+        # Add usage on final chunk
+        if output.finish_reason:
+            chunk["usage"] = self._build_completion_usage(request_output)
+
+        return chunk
+
+    def _format_image_chunk(
+        self,
+        images: list,
+        request_id: str,
+    ) -> Dict[str, Any] | None:
+        """Format image output as OpenAI chat completion chunk with base64 data URLs."""
+        import base64
+        from io import BytesIO
+
+        if not images:
+            return self._error_chunk(request_id, "No images generated")
+
+        # Convert images to base64 data URLs
+        data_urls = []
+        for idx, img in enumerate(images):
+            # Convert PIL image to base64
+            buffer = BytesIO()
+            img.save(buffer, format="PNG")
+            img_base64 = base64.b64encode(buffer.getvalue()).decode("utf-8")
+
+            # Create data URL (can be opened directly in browser)
+            data_url = f"data:image/png;base64,{img_base64}"
+            data_urls.append(data_url)
+            logger.info(f"Generated image {idx} for request {request_id}")
+
+        chunk = {
+            "id": request_id,
+            "created": int(time.time()),
+            "object": "chat.completion.chunk",
+            "model": self.config.served_model_name or self.config.model,
+            "choices": [
+                {
+                    "index": 0,
+                    "delta": {
+                        "role": "assistant",
+                        "content": [
+                            {"type": "image_url", "image_url": {"url": data_url}}
+                            for data_url in data_urls
+                        ],
+                    },
+                    "finish_reason": "stop",
+                }
+            ],
+        }
+
+        return chunk
+
+    def _extract_text_prompt(self, request: Dict[str, Any]) -> str | None:
+        """Extract text prompt from request."""
+
+        # OpenAI messages format - extract text content only
+        messages = request.get("messages", [])
+        # Assumes single user message
+        for message in messages:
+            if message.get("role") == "user":
+                return message.get("content")
+        return ""
 
     def _build_sampling_params(self, request: Dict[str, Any]) -> SamplingParams:
         """Build sampling params using shared handler utility."""
@@ -150,6 +291,25 @@ class OmniHandler(BaseWorkerHandler):
             request, self.default_sampling_params, self.model_max_len
         )
 
+    def _error_chunk(self, request_id: str, error_message: str) -> Dict[str, Any]:
+        """Create an error chunk in OpenAI format."""
+        return {
+            "id": request_id,
+            "created": int(time.time()),
+            "object": "chat.completion.chunk",
+            "model": self.config.served_model_name or self.config.model,
+            "choices": [
+                {
+                    "index": 0,
+                    "delta": {
+                        "role": "assistant",
+                        "content": f"Error: {error_message}",
+                    },
+                    "finish_reason": "error",
+                }
+            ],
+        }
+
     def cleanup(self):
         """Cleanup AsyncOmni orchestrator resources."""
         try:

docs/backends/vllm/vllm-omni.md

+<!--
+SPDX-FileCopyrightText: Copyright (c) 2025-2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+SPDX-License-Identifier: Apache-2.0
+-->
+
+# [Experimental] Running Omni Models with vLLM
+
+Dynamo supports omni (multimodal generation) models via the [vLLM-Omni](https://github.com/vllm-project/vllm-omni) backend. This enables multi-stage pipelines for tasks like text-to-text and text-to-image generation through an OpenAI-compatible API.
+
+## Prerequisites
+
+This guide assumes familiarity with deploying Dynamo with vLLM as described in [README.md](/docs/backends/vllm/README.md).
+
+## Quick Start
+
+### Text-to-Text
+
+Launch an aggregated deployment (frontend + omni worker) using the provided script:
+
+```bash
+bash examples/backends/vllm/launch/agg_omni.sh
+```
+
+This starts `Qwen/Qwen2.5-Omni-7B` with a single-stage thinker config on one GPU. Override the model with:
+
+```bash
+bash examples/backends/vllm/launch/agg_omni.sh --model <your-model>
+```
+
+Test the deployment:
+
+```bash
+curl -X POST http://localhost:8000/v1/chat/completions \
+  -H "Content-Type: application/json" \
+  -d '{
+    "model": "Qwen/Qwen2.5-Omni-7B",
+    "messages": [{"role": "user", "content": "What is 2+2?"}],
+    "max_tokens": 50,
+    "stream": false
+  }'
+```
+
+### Text-to-Image
+
+Text-to-image uses vLLM-Omni's built-in default stage configs (no custom YAML needed). Launch without a stage config path so vLLM-Omni loads the model's default multi-stage pipeline:
+
+```bash
+# Start frontend
+python -m dynamo.frontend &
+
+# Start omni worker (vLLM-Omni loads default stage configs for the model)
+DYN_SYSTEM_PORT=8081 python -m dynamo.vllm \
+  --model <your-text-to-image-model> \
+  --omni \
+  --connector none
+```
+
+Images are returned as base64-encoded PNGs in the response:
+
+```bash
+curl -X POST http://localhost:8000/v1/chat/completions \
+  -H "Content-Type: application/json" \
+  -d '{
+    "model": "<your-text-to-image-model>",
+    "messages": [{"role": "user", "content": "A cat sitting on a windowsill"}],
+    "stream": false
+  }'
+```
+
+The response contains image data URLs in the content field:
+
+```json
+{
+  "choices": [{
+    "delta": {
+      "content": [
+        {"type": "image_url", "image_url": {"url": "data:image/png;base64,..."}}
+      ]
+    }
+  }]
+}
+```
+
+## Key Flags
+
+| Flag | Description |
+|------|-------------|
+| `--omni` | Enable vLLM-Omni orchestrator (required) |
+| `--stage-configs-path <path>` | Path to stage config YAML (optional; vLLM-Omni uses model defaults if omitted) |
+| `--connector none` | Disable KV connector (recommended for omni) |
+
+## Stage Configuration
+
+Omni pipelines are configured via YAML stage configs. See [`examples/backends/vllm/launch/stage_configs/single_stage_llm.yaml`](/examples/backends/vllm/launch/stage_configs/single_stage_llm.yaml) for an example. Key fields:
+
+- **`model_stage`**: Pipeline stage name (e.g., `thinker`, `talker`, `code2wav`)
+- **`final_output_type`**: Output format — `text` or `image`
+- **`is_comprehension`**: Whether this stage processes input text/multimodal content
+
+For full documentation on stage config format, supported fields, and multi-stage pipeline examples, see the [vLLM-Omni Stage Configs documentation](https://docs.vllm.ai/projects/vllm-omni/en/latest/configuration/stage_configs/).
+
+## Current Limitations
+
+- Only text prompts are supported (no multimodal input yet)
+- KV cache events are not published for omni workers

docs/hidden_toctree.rst

@@ -42,6 +42,7 @@
    backends/vllm/multi-node.md
    backends/vllm/prometheus.md
    backends/vllm/prompt-embeddings.md
+   backends/vllm/vllm-omni.md
 
    backends/sglang/expert-distribution-eplb.md
    backends/sglang/gpt-oss.md

examples/backends/vllm/launch/stage_configs/single_stage_llm.yaml

@@ -36,7 +36,7 @@ stage_args:
       temperature: 0.0
       top_p: 1.0
       top_k: -1
-      max_tokens: 2048
+      max_tokens: 20
       repetition_penalty: 1.1
       seed: 42
-      detokenize: false  # Token-based processing for Dynamo
+      detokenize: true  # Token-based processing for Dynamo

lib/async-openai/src/types/chat.rs

@@ -375,6 +375,77 @@ pub enum ChatCompletionRequestToolMessageContent {
     Array(Vec<ChatCompletionRequestToolMessageContentPart>),
 }
 
+// Omni Specific Multimodal Content Types
+// These types are used for assistant message responses that contain multimodal content
+
+/// Response content part for text in assistant messages
+#[derive(ToSchema, Clone, Serialize, Debug, Deserialize, PartialEq)]
+pub struct ChatCompletionResponseContentPartText {
+    pub text: String,
+}
+
+/// Response content part for image URLs in assistant messages
+#[derive(ToSchema, Clone, Serialize, Debug, Deserialize, PartialEq)]
+pub struct ChatCompletionResponseContentPartImageUrl {
+    pub image_url: ImageUrlResponse,
+}
+
+/// Response content part for video URLs in assistant messages
+#[derive(ToSchema, Clone, Serialize, Debug, Deserialize, PartialEq)]
+pub struct ChatCompletionResponseContentPartVideoUrl {
+    pub video_url: VideoUrlResponse,
+}
+
+/// Response content part for audio URLs in assistant messages
+#[derive(ToSchema, Clone, Serialize, Debug, Deserialize, PartialEq)]
+pub struct ChatCompletionResponseContentPartAudioUrl {
+    pub audio_url: AudioUrlResponse,
+}
+
+/// Image URL in response messages (supports data URLs with base64)
+#[derive(ToSchema, Clone, Serialize, Debug, Deserialize, PartialEq)]
+pub struct ImageUrlResponse {
+    /// The URL of the image, either a URL or a data URL (data:image/png;base64,...)
+    pub url: String,
+    /// Optional detail level (for compatibility with OpenAI)
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub detail: Option<String>,
+}
+
+/// Video URL in response messages
+#[derive(ToSchema, Clone, Serialize, Debug, Deserialize, PartialEq)]
+pub struct VideoUrlResponse {
+    /// The URL of the video, either a URL or a data URL
+    pub url: String,
+}
+
+/// Audio URL in response messages
+#[derive(ToSchema, Clone, Serialize, Debug, Deserialize, PartialEq)]
+pub struct AudioUrlResponse {
+    /// The URL of the audio, either a URL or a data URL
+    pub url: String,
+}
+
+/// Content parts for assistant responses supporting multiple modalities (text, images, videos, audio)
+#[derive(ToSchema, Clone, Serialize, Debug, Deserialize, PartialEq)]
+#[serde(tag = "type", rename_all = "snake_case")]
+pub enum ChatCompletionResponseContentPart {
+    Text(ChatCompletionResponseContentPartText),
+    ImageUrl(ChatCompletionResponseContentPartImageUrl),
+    VideoUrl(ChatCompletionResponseContentPartVideoUrl),
+    AudioUrl(ChatCompletionResponseContentPartAudioUrl),
+}
+
+/// Assistant message content - can be a simple string or an array of content parts
+#[derive(ToSchema, Clone, Serialize, Debug, Deserialize, PartialEq)]
+#[serde(untagged)]
+pub enum ChatCompletionMessageContent {
+    /// Simple text content (backward compatible)
+    Text(String),
+    /// Array of content parts (for multimodal responses)
+    Parts(Vec<ChatCompletionResponseContentPart>),
+}
+
 #[derive(ToSchema, Debug, Serialize, Deserialize, Default, Clone, Builder, PartialEq)]
 #[builder(name = "ChatCompletionRequestUserMessageArgs")]
 #[builder(pattern = "mutable")]
@@ -486,9 +557,9 @@ pub struct ChatCompletionResponseMessageAudio {
 /// A chat completion message generated by the model.
 #[derive(ToSchema, Debug, Deserialize, Serialize, Clone, PartialEq)]
 pub struct ChatCompletionResponseMessage {
-    /// The contents of the message.
+    /// The contents of the message - can be a string or array of content parts
     #[serde(skip_serializing_if = "Option::is_none")]
-    pub content: Option<String>,
+    pub content: Option<ChatCompletionMessageContent>,
     /// The refusal message generated by the model.
     #[serde(skip_serializing_if = "Option::is_none")]
     pub refusal: Option<String>,
@@ -1094,8 +1165,8 @@ pub struct ChatCompletionMessageToolCallChunk {
 /// A chat completion delta generated by streamed model responses.
 #[derive(ToSchema, Debug, Deserialize, Serialize, Clone, PartialEq)]
 pub struct ChatCompletionStreamResponseDelta {
-    /// The contents of the chunk message.
-    pub content: Option<String>,
+    /// The contents of the chunk message - can be a string or array of content parts
+    pub content: Option<ChatCompletionMessageContent>,
     /// Deprecated and replaced by `tool_calls`. The name and arguments of a function that should be called, as generated by the model.
     #[deprecated]
     pub function_call: Option<FunctionCallStream>,

lib/bindings/python/rust/lib.rs

@@ -311,7 +311,7 @@ fn register_llm<'p>(
 
     pyo3_async_runtimes::tokio::future_into_py(py, async move {
         // For TensorBased and Images models, skip HuggingFace downloads and register directly
-        // These model types don't require tokenizers
+        // Images models (vLLM-Omni) handle model loading internally, no tokenizer extraction needed
         if is_tensor_based || is_images {
             let model_name = model_name.unwrap_or_else(|| source_path.clone());
             let mut card = llm_rs::model_card::ModelDeploymentCard::with_name_only(&model_name);

lib/engines/mistralrs/src/lib.rs

@@ -405,7 +405,7 @@ impl
                                 delta: dynamo_async_openai::types::ChatCompletionStreamResponseDelta{
                                     //role: c.choices[0].delta.role,
                                     role: Some(dynamo_async_openai::types::Role::Assistant),
-                                    content: Some(from_assistant),
+                                    content: Some(dynamo_async_openai::types::ChatCompletionMessageContent::Text(from_assistant)),
                                     tool_calls: None,
                                     refusal: None,
                                     function_call: None,

lib/llm/src/audit/stream.rs

@@ -246,7 +246,8 @@ pub fn final_response_to_one_chunk_stream(
 mod tests {
     use super::*;
     use dynamo_async_openai::types::{
-        ChatChoiceStream, ChatCompletionStreamResponseDelta, FinishReason, Role,
+        ChatChoiceStream, ChatCompletionMessageContent, ChatCompletionStreamResponseDelta,
+        FinishReason, Role,
     };
     use futures::StreamExt;
     use futures::stream;
@@ -261,7 +262,7 @@ mod tests {
             index,
             delta: ChatCompletionStreamResponseDelta {
                 role: Some(Role::Assistant),
-                content: Some(content),
+                content: Some(ChatCompletionMessageContent::Text(content)),
                 tool_calls: None,
                 function_call: None,
                 refusal: None,
@@ -337,7 +338,10 @@ mod tests {
             .as_ref()
             .and_then(|d| d.choices.first())
             .and_then(|c| c.delta.content.as_ref())
-            .cloned()
+            .and_then(|content| match content {
+                ChatCompletionMessageContent::Text(text) => Some(text.clone()),
+                ChatCompletionMessageContent::Parts(_) => None,
+            })
             .unwrap_or_default()
     }
 
@@ -423,7 +427,9 @@ mod tests {
                         index: 0,
                         delta: ChatCompletionStreamResponseDelta {
                             role: Some(Role::Assistant),
-                            content: Some("Content".to_string()),
+                            content: Some(ChatCompletionMessageContent::Text(
+                                "Content".to_string(),
+                            )),
                             tool_calls: None,
                             function_call: None,
                             refusal: None,

lib/llm/src/discovery/model_manager.rs

@@ -169,6 +169,7 @@ impl ModelManager {
             .chain(self.list_completions_models())
             .chain(self.list_embeddings_models())
             .chain(self.list_tensor_models())
+            .chain(self.list_images_models())
             .chain(self.list_prefill_models())
             .collect()
     }
@@ -193,6 +194,10 @@ impl ModelManager {
         self.prefill_engines.read().list()
     }
 
+    pub fn list_images_models(&self) -> Vec<String> {
+        self.images_engines.read().list()
+    }
+
     pub fn add_completions_model(
         &self,
         model: &str,

lib/llm/src/discovery/watcher.rs

@@ -71,6 +71,7 @@ const ALL_MODEL_TYPES: &[ModelType] = &[
     ModelType::Completions,
     ModelType::Embedding,
     ModelType::TensorBased,
+    ModelType::Images,
     ModelType::Prefill,
 ];
 
@@ -284,12 +285,14 @@ impl ModelWatcher {
         let completions_model_remove_err = self.manager.remove_completions_model(&model_name);
         let embeddings_model_remove_err = self.manager.remove_embeddings_model(&model_name);
         let tensor_model_remove_err = self.manager.remove_tensor_model(&model_name);
+        let images_model_remove_err = self.manager.remove_images_model(&model_name);
         let prefill_model_remove_err = self.manager.remove_prefill_model(&model_name);
 
         let mut chat_model_removed = false;
         let mut completions_model_removed = false;
         let mut embeddings_model_removed = false;
         let mut tensor_model_removed = false;
+        let mut images_model_removed = false;
         let mut prefill_model_removed = false;
 
         if chat_model_remove_err.is_ok() && self.manager.list_chat_completions_models().is_empty() {
@@ -305,6 +308,9 @@ impl ModelWatcher {
         if tensor_model_remove_err.is_ok() && self.manager.list_tensor_models().is_empty() {
             tensor_model_removed = true;
         }
+        if images_model_remove_err.is_ok() && self.manager.list_images_models().is_empty() {
+            images_model_removed = true;
+        }
         if prefill_model_remove_err.is_ok() && self.manager.list_prefill_models().is_empty() {
             prefill_model_removed = true;
         }
@@ -313,15 +319,17 @@ impl ModelWatcher {
             && !completions_model_removed
             && !embeddings_model_removed
             && !tensor_model_removed
+            && !images_model_removed
             && !prefill_model_removed
         {
             tracing::debug!(
-                "No updates to send for model {}: chat_model_removed: {}, completions_model_removed: {}, embeddings_model_removed: {}, tensor_model_removed: {}, prefill_model_removed: {}",
+                "No updates to send for model {}: chat_model_removed: {}, completions_model_removed: {}, embeddings_model_removed: {}, tensor_model_removed: {}, images_model_removed: {}, prefill_model_removed: {}",
                 model_name,
                 chat_model_removed,
                 completions_model_removed,
                 embeddings_model_removed,
                 tensor_model_removed,
+                images_model_removed,
                 prefill_model_removed
             );
         } else {
@@ -330,6 +338,7 @@ impl ModelWatcher {
                     || (completions_model_removed && *model_type == ModelType::Completions)
                     || (embeddings_model_removed && *model_type == ModelType::Embedding)
                     || (tensor_model_removed && *model_type == ModelType::TensorBased)
+                    || (images_model_removed && *model_type == ModelType::Images)
                     || (prefill_model_removed && *model_type == ModelType::Prefill))
                     && let Some(tx) = &self.model_update_tx
                 {
@@ -614,7 +623,7 @@ impl ModelWatcher {
             self.manager
                 .add_embeddings_model(card.name(), checksum, embedding_engine)?;
         } else if card.model_input == ModelInput::Tensor && card.model_type.supports_tensor() {
-            // Case 5: Tensor + Tensor (non-LLM)
+            // Case 6: Tensor + TensorBased (non-LLM)
             // No KV cache concepts - not an LLM model
             let push_router = PushRouter::<
                 NvCreateTensorRequest,
@@ -627,18 +636,31 @@ impl ModelWatcher {
             self.manager
                 .add_tensor_model(card.name(), checksum, engine)?;
         } else if card.model_input == ModelInput::Text && card.model_type.supports_images() {
-            // Case: Text + Images (diffusion models)
-            // Takes text prompts as input, generates images
-            let push_router = PushRouter::<
+            // Case: Text + Images (e.g. vLLM-Omni, diffusion models)
+            // Takes text prompts as input, generates images. Images models also support
+            // chat completions (see model_type.rs as_endpoint_types).
+            let images_router = PushRouter::<
                 NvCreateImageRequest,
                 Annotated<NvImagesResponse>,
             >::from_client_with_threshold(
-                client, self.router_config.router_mode, None, None
+                client.clone(), self.router_config.router_mode, None, None
             )
             .await?;
-            let engine = Arc::new(push_router);
             self.manager
-                .add_images_model(card.name(), checksum, engine)?;
+                .add_images_model(card.name(), checksum, Arc::new(images_router))?;
+
+            let chat_router = PushRouter::<
+                NvCreateChatCompletionRequest,
+                Annotated<NvCreateChatCompletionStreamResponse>,
+            >::from_client_with_threshold(
+                client, self.router_config.router_mode, None, None
+            )
+            .await?;
+            self.manager.add_chat_completions_model(
+                card.name(),
+                checksum,
+                Arc::new(chat_router),
+            )?;
         } else if card.model_type.supports_prefill() {
             // Case 6: Prefill
             // Guardrail: Verify model_input is Tokens

lib/llm/src/entrypoint/input/batch.rs

@@ -7,7 +7,7 @@ use crate::types::openai::chat_completions::{
     NvCreateChatCompletionRequest, OpenAIChatCompletionsStreamingEngine,
 };
 use anyhow::Context as _;
-use dynamo_async_openai::types::FinishReason;
+use dynamo_async_openai::types::{ChatCompletionMessageContent, FinishReason};
 use dynamo_runtime::{DistributedRuntime, pipeline::Context, runtime::CancellationToken};
 use futures::StreamExt;
 use serde::{Deserialize, Serialize};
@@ -241,7 +241,15 @@ async fn evaluate(
                 let choice = data.choices.first();
                 let chat_comp = choice.as_ref().unwrap();
                 if let Some(c) = &chat_comp.delta.content {
-                    output += c;
+                    match c {
+                        ChatCompletionMessageContent::Text(text) => {
+                            output += text;
+                        }
+                        ChatCompletionMessageContent::Parts(_) => {
+                            // Multimodal content - skip for now in batch processing
+                            // (ayushag) TODO: Handle multimodal content in batch mode
+                        }
+                    }
                 }
                 entry.finish_reason = chat_comp.finish_reason;
                 if chat_comp.finish_reason.is_some() {

lib/llm/src/entrypoint/input/text.rs

 // SPDX-FileCopyrightText: Copyright (c) 2024-2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
 // SPDX-License-Identifier: Apache-2.0
 
+use crate::entrypoint::EngineConfig;
+use crate::entrypoint::input::common;
 use crate::request_template::RequestTemplate;
 use crate::types::openai::chat_completions::{
     NvCreateChatCompletionRequest, OpenAIChatCompletionsStreamingEngine,
 };
+use dynamo_async_openai::types::ChatCompletionMessageContent;
 use dynamo_runtime::DistributedRuntime;
 use dynamo_runtime::pipeline::Context;
 use futures::StreamExt;
 use std::io::{ErrorKind, Write};
 
-use crate::entrypoint::EngineConfig;
-use crate::entrypoint::input::common;
-
 /// Max response tokens for each single query. Must be less than model context size.
 /// TODO: Cmd line flag to overwrite this
 const MAX_TOKENS: u32 = 8192;
@@ -140,9 +140,19 @@ async fn main_loop(
                     let entry = data.choices.first();
                     let chat_comp = entry.as_ref().unwrap();
                     if let Some(c) = &chat_comp.delta.content {
-                        let _ = stdout.write(c.as_bytes());
-                        let _ = stdout.flush();
-                        assistant_message += c;
+                        match c {
+                            ChatCompletionMessageContent::Text(text) => {
+                                let _ = stdout.write(text.as_bytes());
+                                let _ = stdout.flush();
+                                assistant_message += text;
+                            }
+                            ChatCompletionMessageContent::Parts(_) => {
+                                // (ayushag) TODO: Handle multimodal content for multiturn conversations
+                                // Multimodal content - for now just print a placeholder
+                                let _ = stdout.write(b"[multimodal content]");
+                                let _ = stdout.flush();
+                            }
+                        }
                     }
                     if let Some(reason) = chat_comp.finish_reason {
                         tracing::trace!("finish reason: {reason:?}");

lib/llm/src/mocker.rs

@@ -384,6 +384,8 @@ impl AsyncEngine<SingleIn<PreprocessedRequest>, ManyOut<LLMEngineOutput>, Error>
                             token_ids: vec![token_id],
                             tokens: None,  // Let backend handle detokenization
                             text: None,
+                            output_type: Default::default(),
+                            content_parts: None,
                             cum_log_probs: None,
                             log_probs: None,
                             top_logprobs: None,

lib/llm/src/model_type.rs

@@ -126,8 +126,10 @@ impl ModelType {
         if self.contains(Self::Embedding) {
             endpoint_types.push(crate::endpoint_type::EndpointType::Embedding);
         }
+        // Images models support both chat and completions endpoints
         if self.contains(Self::Images) {
             endpoint_types.push(crate::endpoint_type::EndpointType::Images);
+            endpoint_types.push(crate::endpoint_type::EndpointType::Chat);
         }
         // [gluo NOTE] ModelType::Tensor doesn't map to any endpoint type,
         // current use of endpoint type is LLM specific and so does the HTTP

lib/llm/src/perf/logprobs.rs

@@ -953,7 +953,11 @@ mod tests {
             choices: vec![ChatChoiceStream {
                 index: 0,
                 delta: ChatCompletionStreamResponseDelta {
-                    content: Some("test".to_string()),
+                    content: Some(
+                        dynamo_async_openai::types::ChatCompletionMessageContent::Text(
+                            "test".to_string(),
+                        ),
+                    ),
                     function_call: None,
                     tool_calls: None,
                     role: Some(Role::Assistant),
@@ -987,7 +991,11 @@ mod tests {
             .map(|(i, token_logprobs)| ChatChoiceStream {
                 index: i as u32,
                 delta: ChatCompletionStreamResponseDelta {
-                    content: Some("test".to_string()),
+                    content: Some(
+                        dynamo_async_openai::types::ChatCompletionMessageContent::Text(
+                            "test".to_string(),
+                        ),
+                    ),
                     function_call: None,
                     tool_calls: None,
                     role: Some(Role::Assistant),
@@ -1337,7 +1345,11 @@ mod tests {
             choices: vec![ChatChoiceStream {
                 index: 0,
                 delta: ChatCompletionStreamResponseDelta {
-                    content: Some("test".to_string()),
+                    content: Some(
+                        dynamo_async_openai::types::ChatCompletionMessageContent::Text(
+                            "test".to_string(),
+                        ),
+                    ),
                     function_call: None,
                     tool_calls: None,
                     role: Some(Role::Assistant),

lib/llm/src/preprocessor.rs

@@ -945,14 +945,23 @@ impl OpenAIPreprocessor {
                     response.map_data(|mut data| {
                         // Process all choices, not just the first one
                         for choice in data.choices.iter_mut() {
-                            if let Some(text) = choice.delta.content.as_ref() {
+                            // Reasoning parsing only applies to text content
+                            if let Some(
+                                dynamo_async_openai::types::ChatCompletionMessageContent::Text(
+                                    text,
+                                ),
+                            ) = choice.delta.content.as_ref()
+                            {
                                 let parser_result =
                                     parser.parse_reasoning_streaming_incremental(text, &[]);
 
                                 // Update this specific choice with parsed content
-                                choice.delta.content = parser_result.get_some_normal_text();
+                                choice.delta.content = parser_result.get_some_normal_text().map(
+                                    dynamo_async_openai::types::ChatCompletionMessageContent::Text,
+                                );
                                 choice.delta.reasoning_content = parser_result.get_some_reasoning();
                             }
+                            // For multimodal content, pass through unchanged
                         }
                         Ok(data)
                     })

lib/llm/src/protocols/common/llm_backend.rs

@@ -13,6 +13,45 @@ use dynamo_runtime::protocols::maybe_error::MaybeError;
 pub type TokenType = Option<String>;
 pub type LogProbs = Vec<f64>;
 
+/// Output type discriminator for different modalities
+#[derive(Serialize, Deserialize, Debug, Clone, Copy, PartialEq, Eq, Default)]
+#[serde(rename_all = "lowercase")]
+pub enum OutputType {
+    #[default]
+    Text,
+    Image,
+    Video,
+    Audio,
+}
+
+/// Image URL data for responses
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq)]
+pub struct ImageUrlData {
+    pub url: String,
+}
+
+/// Video URL data for responses
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq)]
+pub struct VideoUrlData {
+    pub url: String,
+}
+
+/// Audio URL data for responses
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq)]
+pub struct AudioUrlData {
+    pub url: String,
+}
+
+/// Content part for multimodal outputs (internal representation)
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq)]
+#[serde(tag = "type", rename_all = "snake_case")]
+pub enum ContentPart {
+    Text { text: String },
+    ImageUrl { image_url: ImageUrlData },
+    VideoUrl { video_url: VideoUrlData },
+    AudioUrl { audio_url: AudioUrlData },
+}
+
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq)]
 pub struct TopLogprob {
     pub rank: u32,
@@ -86,6 +125,14 @@ pub struct LLMEngineOutput {
     // decoded text -
     pub text: Option<String>,
 
+    /// Output type discriminator (text, image, video, audio)
+    #[serde(default)]
+    pub output_type: OutputType,
+
+    /// Multimodal content parts (for non-text outputs)
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub content_parts: Option<Vec<ContentPart>>,
+
     /// cumulative log probabilities
     pub cum_log_probs: Option<f64>,
 
@@ -125,6 +172,8 @@ impl LLMEngineOutput {
             token_ids: vec![],
             tokens: None,
             text: None,
+            output_type: OutputType::default(),
+            content_parts: None,
             cum_log_probs: None,
             log_probs: None,
             top_logprobs: None,
@@ -142,6 +191,8 @@ impl LLMEngineOutput {
             token_ids: vec![],
             tokens: None,
             text: None,
+            output_type: OutputType::default(),
+            content_parts: None,
             cum_log_probs: None,
             log_probs: None,
             finish_reason: Some(FinishReason::Stop),
@@ -159,6 +210,8 @@ impl LLMEngineOutput {
             token_ids: vec![],
             tokens: None,
             text: None,
+            output_type: OutputType::default(),
+            content_parts: None,
             cum_log_probs: None,
             log_probs: None,
             top_logprobs: None,
@@ -176,6 +229,8 @@ impl LLMEngineOutput {
             token_ids: vec![],
             tokens: None,
             text: None,
+            output_type: OutputType::default(),
+            content_parts: None,
             cum_log_probs: None,
             log_probs: None,
             top_logprobs: None,

lib/llm/src/protocols/openai/chat_completions/aggregator.rs

@@ -12,7 +12,7 @@ use crate::protocols::{
     openai::ParsingOptions,
 };
 
-use dynamo_async_openai::types::StopReason;
+use dynamo_async_openai::types::{ChatCompletionMessageContent, StopReason};
 use dynamo_runtime::engine::DataStream;
 
 /// Aggregates a stream of [`NvCreateChatCompletionStreamResponse`]s into a single
@@ -59,6 +59,9 @@ struct DeltaChoice {
 
     /// Optional reasoning content for the chat choice.
     reasoning_content: Option<String>,
+
+    /// Accumulated content parts for multimodal responses
+    content_parts: Vec<dynamo_async_openai::types::ChatCompletionResponseContentPart>,
 }
 
 impl Default for DeltaAggregator {
@@ -166,10 +169,18 @@ impl DeltaAggregator {
                                     logprobs: None,
                                     tool_calls: None,
                                     reasoning_content: None,
+                                    content_parts: Vec::new(),
                                 });
-                        // Append content if available.
+                        // Handle content based on type
                         if let Some(content) = &choice.delta.content {
-                            state_choice.text.push_str(content);
+                            match content {
+                                ChatCompletionMessageContent::Text(text) => {
+                                    state_choice.text.push_str(text);
+                                }
+                                ChatCompletionMessageContent::Parts(parts) => {
+                                    state_choice.content_parts.extend(parts.clone());
+                                }
+                            }
                         }
 
                         if let Some(reasoning_content) = &choice.delta.reasoning_content {
@@ -289,14 +300,21 @@ impl From<DeltaChoice> for dynamo_async_openai::types::ChatChoice {
             delta.finish_reason
         };
 
+        // Determine content format based on what we accumulated
+        let content = if !delta.content_parts.is_empty() {
+            // Multimodal response with content parts
+            Some(ChatCompletionMessageContent::Parts(delta.content_parts))
+        } else if !delta.text.is_empty() {
+            // Text-only response (backward compatible)
+            Some(ChatCompletionMessageContent::Text(delta.text))
+        } else {
+            None
+        };
+
         dynamo_async_openai::types::ChatChoice {
             message: dynamo_async_openai::types::ChatCompletionResponseMessage {
                 role: delta.role.expect("delta should have a Role"),
-                content: if delta.text.is_empty() {
-                    None
-                } else {
-                    Some(delta.text)
-                },
+                content,
                 tool_calls: delta.tool_calls,
                 refusal: None,
                 function_call: None,
@@ -396,7 +414,7 @@ mod tests {
         };
 
         let delta = dynamo_async_openai::types::ChatCompletionStreamResponseDelta {
-            content: Some(text.to_string()),
+            content: Some(ChatCompletionMessageContent::Text(text.to_string())),
             function_call: None,
             tool_calls: tool_call_chunks,
             role,
@@ -496,7 +514,10 @@ mod tests {
         assert_eq!(response.choices.len(), 1);
         let choice = &response.choices[0];
         assert_eq!(choice.index, 0);
-        assert_eq!(choice.message.content.as_ref().unwrap(), "Hello,");
+        assert_eq!(
+            choice.message.content.as_ref().unwrap(),
+            &ChatCompletionMessageContent::Text("Hello,".to_string())
+        );
         assert!(choice.finish_reason.is_none());
         assert_eq!(choice.message.role, dynamo_async_openai::types::Role::User);
         assert!(response.service_tier.is_none());
@@ -539,7 +560,10 @@ mod tests {
         assert_eq!(response.choices.len(), 1);
         let choice = &response.choices[0];
         assert_eq!(choice.index, 0);
-        assert_eq!(choice.message.content.as_ref().unwrap(), "Hello, world!");
+        assert_eq!(
+            choice.message.content.as_ref().unwrap(),
+            &ChatCompletionMessageContent::Text("Hello, world!".to_string())
+        );
         assert_eq!(
             choice.finish_reason,
             Some(dynamo_async_openai::types::FinishReason::Stop)
@@ -605,7 +629,12 @@ mod tests {
         let choice = &response.choices[0];
 
         assert_eq!(choice.index, 0);
-        assert_eq!(choice.message.content.as_deref(), Some("Hello world"));
+        assert_eq!(
+            choice.message.content.as_ref(),
+            Some(&ChatCompletionMessageContent::Text(
+                "Hello world".to_string()
+            ))
+        );
         assert_eq!(
             choice.finish_reason,
             Some(dynamo_async_openai::types::FinishReason::Stop)
@@ -630,7 +659,7 @@ mod tests {
                     index: 0,
                     delta: dynamo_async_openai::types::ChatCompletionStreamResponseDelta {
                         role: Some(dynamo_async_openai::types::Role::Assistant),
-                        content: Some("Choice 0".to_string()),
+                        content: Some(ChatCompletionMessageContent::Text("Choice 0".to_string())),
                         function_call: None,
                         tool_calls: None,
                         refusal: None,
@@ -644,7 +673,7 @@ mod tests {
                     index: 1,
                     delta: dynamo_async_openai::types::ChatCompletionStreamResponseDelta {
                         role: Some(dynamo_async_openai::types::Role::Assistant),
-                        content: Some("Choice 1".to_string()),
+                        content: Some(ChatCompletionMessageContent::Text("Choice 1".to_string())),
                         function_call: None,
                         tool_calls: None,
                         refusal: None,
@@ -680,7 +709,10 @@ mod tests {
         response.choices.sort_by(|a, b| a.index.cmp(&b.index)); // Ensure the choices are ordered
         let choice0 = &response.choices[0];
         assert_eq!(choice0.index, 0);
-        assert_eq!(choice0.message.content.as_ref().unwrap(), "Choice 0");
+        assert_eq!(
+            choice0.message.content.as_ref().unwrap(),
+            &ChatCompletionMessageContent::Text("Choice 0".to_string())
+        );
         assert_eq!(
             choice0.finish_reason,
             Some(dynamo_async_openai::types::FinishReason::Stop)
@@ -692,7 +724,10 @@ mod tests {
 
         let choice1 = &response.choices[1];
         assert_eq!(choice1.index, 1);
-        assert_eq!(choice1.message.content.as_ref().unwrap(), "Choice 1");
+        assert_eq!(
+            choice1.message.content.as_ref().unwrap(),
+            &ChatCompletionMessageContent::Text("Choice 1".to_string())
+        );
         assert_eq!(
             choice1.finish_reason,
             Some(dynamo_async_openai::types::FinishReason::Stop)
@@ -962,7 +997,9 @@ mod tests {
 
         assert_eq!(
             choice.message.content.as_ref().unwrap(),
-            "Hey Dude ! What's the weather in San Francisco in Fahrenheit?"
+            &ChatCompletionMessageContent::Text(
+                "Hey Dude ! What's the weather in San Francisco in Fahrenheit?".to_string()
+            )
         );
 
         // The finish_reason should be ToolCalls